| From: | Martijn van Oosterhout <kleptog(at)svana(dot)org> |
|---|---|
| To: | Simon Riggs <simon(at)2ndquadrant(dot)com> |
| Cc: | Bruce Momjian <bruce(at)momjian(dot)us>, PostgreSQL-development <pgsql-hackers(at)postgreSQL(dot)org>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Kevin Grittner <Kevin(dot)Grittner(at)wicourts(dot)gov>, "Jim C(dot) Nasby" <jim(at)nasby(dot)net>, ITAGAKI Takahiro <itagaki(dot)takahiro(at)oss(dot)ntt(dot)co(dot)jp> |
| Subject: | Re: Load distributed checkpoint |
| Date: | 2006-12-27 22:26:45 |
| Message-ID: | 20061227222645.GC12448@svana.org |
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| Lists: | pgsql-hackers pgsql-patches |
On Wed, Dec 27, 2006 at 09:24:06PM +0000, Simon Riggs wrote:
> On Fri, 2006-12-22 at 13:53 -0500, Bruce Momjian wrote:
>
> > I assume other kernels have similar I/O smoothing, so that data sent to
> > the kernel via write() gets to disk within 30 seconds.
> >
> > I assume write() is not our checkpoint performance problem, but the
> > transfer to disk via fsync().
>
> Well, its correct to say that the transfer to disk is the source of the
> problem, but that doesn't only occur when we fsync(). There are actually
> two disk storms that occur, because of the way the fs cache works. [Ron
> referred to this effect uplist]
As someone looking from the outside:
fsync only works on one file, so presumably the checkpoint process is
opening each file one by one and fsyncing them. Does that make any
difference here? Could you adjust the timing here?
Have a nice day,
--
Martijn van Oosterhout <kleptog(at)svana(dot)org> http://svana.org/kleptog/
> From each according to his ability. To each according to his ability to litigate.
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